I. Field of the Invention
The present invention relates generally to gas phase (vapor) sterilization and, more particularly, to disinfecting and sterilizing devices having elongate, narrow passages or lumens accessible from both ends such as those commonly associated with vascular catheters endoscopes and similar devices. While the entire device must be sterilized, the invention is primarily concerned with the successful sterilization of the more difficult internal surfaces concurrently with sterilization of the exterior. The invention employs techniques that produce a flow of sterilizing gas through the internal passage or passages in a given load (items to be concurrently sterilized) during processing which results in a rapid and complete exposure of internal passage or channel surfaces of each item of the load to the sterilant vapor by transforming each lumen or other channel or passage of interest into a flow channel for the sterilant gas during successive evacuation and pressurization cycles.
II. Related Art
The need to sterilize articles such as medical devices and instruments following manufacture and initial packaging for use or prior to reuse after contacting a patient has long been recognized. Traditional methods of sterilization include immersion of the article or instrument of interest in a sterilizing solution or the use of various techniques involving elevated temperatures. More recently, however, it has been recognized that chemical vapor sterilization at lower temperatures is generally better suited to today's more sensitive and sophisticated instrumentation and materials of construction. Moreover, financial constraints placed generally on medical care providers presently produce situations in which "single-use" items previously discarded after the first patient are now being resterilized and reused.
While vapor sterilization has offered several distinct advantages over other forms, one major disadvantage heretofore associated with the technique involves an inability to conduct sufficient sterilizing vapor to contact the central internal surfaces of rather long and narrow passages such as the lumens of catheters and endoscopes in an expeditious manner. Typically, present systems operate by partially evacuating the sterilization chamber prior to the introduction of the sterilizing material in a repressurization step. The chamber may be subjected to a series of evacuation pressurization cycles in this manner. Complete sterilization of the internal surfaces depends on diffusion of the sterilant gas, which might be ethylene oxide or another material usually diluted in a carrier gas along the passages from the open ends to produce sufficient antimicrobial activity at the midpoint of each narrow passage. Unfortunately, normal diffusion and other mixing techniques are simply too slow to accomplish reliable sterilization at passage midpoints within desired time constraints and this may offset other advantages of vapor sterilization. The problem is documented, for example, in Alfa, M. J., "Changes In Hospital Practice", Biomedical Instrumentation and Technology (September/October 1996) and Alfa, M. J. et al, "Comparison of Ion Plasma, Vaporized Hydrogen Peroxide, and 100% Ethylene Oxide Gas Sterilizer", Infection Control And Hospital Epidemiology (February 1996).
Several ways of overcoming the above disadvantage have been proposed with respect to vapor sterilization of relatively long and narrow passages. In one technique, a closed vessel containing a small amount of a vaporizable antimicrobial fluid is attached to one end of an endoscope or other device lumen. A seal is breached in the vessel and the other end of the lumen is exposed to a reduced pressure. This allows antimicrobial vapor to flow along the length of a lumen from the source toward the open end. Such a technique is shown in U.S. Pat. Nos. 5,580,530 and 5,733,503 to Kowatsch et al and in Jacobs et al (U.S. Pat. No. 4,943,414). Another technique shown in Childers et al (U.S. Pat. No. 5,527,508) discloses a pressure modulation technique using a low vapor pressure chemical vapor sterilant in conjunction with a compression carrier gas to promote diffusion in a pressure modulation cyclic sequence. Meanwhile, manufacturers of these devices have been resorting to drastically extended gas sterilization cycles, sometimes taking days to complete, to insure sterility of their device products.
While these previous techniques have met with some success, there remains a need for a method and system that provides more certain and immediate contact between the sterilizing vapor and the internal passage surfaces, particularly the surfaces nearest the midpoint of the passages, to enable the surfaces to be sterilized in an expeditious manner which need not depend on internal diffusive mixing equilibrium.
With regard to certain terminology used in this specification, definitions seem appropriate. The terms "sterilant gas or sterilant vapor"or "sterilizing gas or sterilizing vapor", as used in this specification, refer to any substance, whether true gas or vapor of a volatile liquid, which is capable of sterilizing the load of interest and which is in the gaseous state under use conditions. It may consist of a single active ingredient or a mixture of ingredients, and may contain inactive diluents or carriers. Also, the term "lumen", "channel", "passage", or the like, refers to any internal passage accessible from both ends which is relatively long in relation to its diameter and therefore difficult to readily sterilize near or at its midpoint by diffusion of a sterilant gas from the ends. "Cassette" refers to any relatively compact package form suitable for containing and adapted to receive any of the class of devices (having integral elongate passages) suitable for sterilization and/or storage in accordance with the invention. The cassettes may be of any convenient shape and are assumed to be of sufficient rigidity to withstand the necessary pressure differential used in the method of the invention and the term includes, without limitation, the common rectangular shaped containers. The term "sterilization" means a sufficient reduction in the live microbe and/or spore population to render the device of interest to be safe for its intended use. This is normally a 7-9 log.sub.10 reduction of the bacteria and/or spore population.
Accordingly, a primary object of the present invention is to provide an improved method of vapor sterilization particularly suited to the sterilization of devices of interest having internal surfaces including relatively long, narrow passages characteristic of the lumens of catheters and endoscopic instruments, together with devices for carrying out the method.
Another object of the present invention is to provide an improved method of vapor sterilization that is based on inducing a reversible positive flow of sterilant vapor throughout the length of a passage of interest to be sterilized.
Yet another object of the present invention is to establish a positive flow of sterilant vapor throughout the length of a passage to be sterilized by inducing an end-to-end pressure differential to an open-ended passage to be sterilized by exposing each end to a different time variable (transient) pressure function to transform the passage into a flow channel and to promote flow therethrough to produce immediate antimicrobial activity along the entire length of the passage.
Still another object of the present invention is to accomplish the method of the invention using only a passive partitioned cassette to contain the device of interest and a vacuum/pressurization chamber to contain the cassette.
Yet still another object of the present invention is to provide a close tolerance passage or gas permeable collar at the partition wall within the cassette so as to achieve sterilization of the area of the device contacting the partition.
A further object of the present invention is to produce a time variable (transient) end-to-end pressure differential in each open-ended passage to be sterilized on a reversing basis.
A still further object of the present invention is to provide a partitioned two-chamber cassette to contain a device having an elongate passage to be sterilized with one end in each chamber having gas permeable accesses in each chamber to be exposed simultaneously to vacuum/pressurization sterilization cycling in which the combination of the relative chamber sizes and permeabilities can be used to determine the time variable pressure difference between the chambers.
These and other objects, as well as these and other features and advantages of the invention, will become apparent to those skilled in the art upon familiarization with the specification, drawings and claims contained herein which are meant to exemplify but not to limit the scope of the present invention in any manner.